Editing Timeline of the universe (section)

== First 20 minutes ==
{{Nature timeline}}

=== Planck epoch ===
* c. 0 seconds (13.799 ± 0.021 [[Bya (unit)|Gya]]): [[Planck epoch]] begins: [[Big Bang]] occurs in which ordinary space and time develop out of a primeval state described by a [[Quantum gravity|quantum theory of gravity]] or "[[Theory of everything]]". All matter and energy of the  universe is contained in a hot, dense point ([[gravitational singularity]])

=== Grand unification epoch ===
* c. 10<sup>−43</sup> seconds:  [[Gravity]] separates and begins operating on the universe—the remaining fundamental forces stabilize into the [[electronuclear force]], also known as the Grand Unified Force or [[Grand Unified Theory]] (GUT), mediated by (the hypothetical) [[X and Y bosons]] which allow early [[matter]] at this stage to fluctuate between [[baryon]] and [[lepton]] states.<ref>
{{cite book
 |author1=Cheng, Ta-Pei |author2=Li, Ling-Fong |year=1983
 |title=Gauge Theory of Elementary Particle Physics
 |url=https://archive.org/details/gaugetheoryeleme00chen_958 |url-access=limited |page=[https://archive.org/details/gaugetheoryeleme00chen_958/page/n443 437]
 |publisher=[[Oxford University Press]]
 |isbn=0-19-851961-3
}}</ref>

=== Inflation ===
* c. 10<sup>−35</sup> seconds: [[cosmic inflation|inflation]], expands the universe by a factor of the order of 10<sup>26</sup> over a time of the order of 10<sup>−33</sup> to 10<sup>−32</sup> seconds. The universe is [[supercooled]] from about 10<sup>27</sup> down to 10<sup>22</sup> kelvin.<ref>Guth, "Phase transitions in the very early universe", in: Hawking, Gibbon, Siklos (eds.), ''The Very Early Universe'' (1985).</ref> 
* c. 10<sup>−32</sup> seconds: Cosmic inflation ends.<ref name="Chow-2008">{{Cite book |last=Chow |first=Tai L. |url=https://www.worldcat.org/title/166358163 |title=Gravity, black holes, and the very early universe: an introduction to general relativity and cosmology |date=2008 |publisher=Springer |isbn=978-0-387-73629-7 |location=New York |oclc=166358163}}</ref>{{rp|193}} The familiar [[elementary particle]]s now form as a soup of hot ionized gas called [[quark–gluon plasma]];

=== Quark epoch ===
* c. 10<sup>−12</sup> seconds: [[Cosmological phase transition#Electroweak phase transition|Electroweak phase transition]]: The [[weak nuclear force]] is now a short-range force as it separates from [[electromagnetic force]], so matter particles can [[Higgs mechanism|acquire mass]] and interact with the [[Higgs Field]]. The [[quark–gluon plasma]] persists ([[Quark epoch]]). The universe cools to 10<sup>15</sup> kelvin.{{cn|date=January 2025}}

=== Quark-hadron transition ===
* c. 10<sup>−6</sup> seconds: As the universe cools to about 10<sup>10</sup> kelvin, a quark-hadron transition takes place in which quarks become [[color confinement|confined]] in more complex particles—[[hadrons]].<ref name=Peacock-1998>{{Cite book |last=Peacock |first=J. A. |url=https://www.cambridge.org/core/product/identifier/9780511804533/type/book |title=Cosmological Physics |date=1998-12-28 |publisher=Cambridge University Press |isbn=978-0-521-41072-4 |edition=1 |doi=10.1017/cbo9780511804533}}</ref>{{rp|305}}

=== Lepton epoch ===
* c. 1 second: [[Lepton epoch]] begins: The universe cools to 10<sup>9</sup> kelvin. At this temperature, the hadrons and antihadrons annihilate each other, leaving behind [[leptons]] and [[antileptons]] – possible disappearance of [[antiquarks]]. Gravity governs the expansion of the universe: neutrinos [[Decoupling (cosmology)|decouple]] from matter creating a [[cosmic neutrino background]].{{cn|date=January 2025}}

=== Photon epoch ===
* c. 10 seconds: [[Photon epoch]] begins: Most leptons and antileptons annihilate each other. As [[electrons]] and [[positrons]] annihilate, a small number of unmatched electrons are left over – disappearance of the positrons.{{cn|date=January 2025}}
* c. 10 seconds: Universe dominated by photons of radiation – ordinary matter particles are coupled to [[light]] and radiation. 
* c. 3 minutes: Primordial [[nucleosynthesis]]: [[nuclear fusion]] begins as [[lithium]] and heavy hydrogen ([[deuterium]]) and [[helium nuclei]] form from protons and neutrons.
* c. 20 minutes: Primordial nucleosynthesis ceases